Wireless communication systems, including cellular phones, paging devices, personal communication services (PCS) systems, and wireless data networks, have become ubiquitous in society. Wireless service providers continually try to create new markets for wireless devices and to expand existing markets by making wireless devices and services cheaper and more reliable. The price of end-user wireless devices, such as cell phones, pagers, PCS systems, and wireless modems, has been driven down to the point where these devices are affordable to nearly everyone and the price of a wireless device is only a small part of the end-user's total cost. To continue to attract new customers, wireless service providers concentrate on reducing infrastructure costs and operating costs, and on increasing handset battery lifetime, while improving quality of service in order to make wireless services cheaper and better.
To maximize usage of the available bandwidth, a number of multiple access technologies have been implemented to allow more than one subscriber to communicate simultaneously with each base station (BS) in a wireless system. These multiple access technologies include time division multiple access (TDMA), frequency division multiple access (FDMA), and code division multiple access (CDMA). These technologies assign each system subscriber to a specific traffic channel that transmits and receives subscriber voice/data signals via a selected time slot, a selected frequency, a selected unique code, or a combination thereof.
CDMA technology is used in wireless computer networks, paging (or wireless messaging) systems, and cellular telephony. In a CDMA system, mobile stations and other access terminals (e.g., pagers, cell phones, laptop PCs with wireless modems) and base stations transmit and receive data on the same frequency in assigned channels that correspond to specific unique orthogonal codes. For example, a mobile station may receive forward channel data signals from a base station that are encoded, formatted, interleaved, spread with a Walsh code and a long pseudo-noise (PN) sequence. In another example, a base station may receive reverse channel data signals from the mobile station that are encoded, block interleaved, modulated, and spread with a spreading code derived from the mobile station identification number prior to transmission by the mobile station. The data symbols following interleaving may be separated into an in-phase (I) data stream and a quadrature (Q) data stream for QPSK modulation of an RF carrier. One such implementation is found in the TIA/EIA-95 CDMA standard (also known as IS-95). Another implementation is the TIA/EIA-2000 standard (also known as IS-2000).
The current generation of cellular phones is used primarily for voice conversations between a subscriber device (or wireless device) and another party through the wireless network. A smaller number of wireless devices are data devices, such as personal digital assistants (PDAs) equipped with cellular/wireless modems. Because the bandwidth for a current generation wireless device is typically limited to a few tens of kilobits per second (kbps), the applications for the current generation of wireless devices are relatively limited. However, this is expected to change in the next (or third) generation of cellular/wireless technology, sometimes referred to as “3G” cellular/wireless, where much greater bandwidth will be available to each wireless device (i.e., one hundred fifty three and six tenths kilobits per second (153.6 kbps) or greater). The higher data rates will make Internet applications for wireless devices much more common. For instance, a 3G cellular telephone (or a PC with a 3G cellular modem) may be used to browse web sites on the Internet, to transmit and receive graphics, to execute streaming audio or video applications, and the like. A much higher percentage of the wireless traffic handled by 3G cellular systems will be Internet protocol (IP) traffic and a lesser percentage will be traditional voice traffic.
Real-time streaming of multimedia content over Internet protocol (IP) networks has become an increasingly common application in recent years. As noted above, 3G wireless networks will provide streaming data (both video and audio) to wireless devices for real time applications. A wide range of interactive and non-interactive multimedia Internet applications, such as news on-demand, live TV viewing, video conferencing, live radio broadcasting (such as Broadcast.com), and the like, will provide “real time” data streaming to wireless devices. Unlike a “downloaded” video file, which may be retrieved first in “non-real” time and viewed or played back later, real time (or streaming) data applications require a data source to encode and to transmit a streaming data signal over a network to a receiver, which must decode and play the signal (video or audio) in real time.
In an IS-2000 system, or in a 1xEV-DO system, or in several of the currently proposed 1xEV-DV systems, packet data is Turbo encoded in blocks using a Turbo encoder. Turbo encoders are well known in the art. See, e.g., C. C. Gumas, “Turbo Codes Rev Up Error-Correcting Performance,” Personal Engineering & Instrumentation News, pp. 61–66, January 1998.
The Turbo encoded packet data is then modulated using either a QPSK RF modulator, or an 8-PSK RF modulator, or a 16-QAM RF modulator. A 64-QAM RF modulator requires a higher signal to noise ratio (SNR) than the signal to noise ratio (SNR) required for a 16-QAM RF modulator. The 64-QAM RF modulator requires, for instance, about nineteen decibels (19 dB) SNR and the 16-QAM RF modulator requires about fifteen decibels (15 dB) SNR.
It is known that 1xEV-DO systems require a 16-QAM RF modulator to support high packet data rates at 2.45 Mbps. To support high packet data rates at 2.45 Mbps in 1xEV-DO systems a mobile station requires a received signal to noise ratio (SNR) of nine and five tenths decibels (9.5 dB) using 16-QAM modulation in order to achieve a one percent (1%) packet data error rate. To support high packet data rates at 2.45 Mbps in 1xEV-DO systems a mobile station requires a received signal to noise ratio (SNR) of eighteen and five tenths decibels (18.5 dB) using 64-QAM modulation in order to achieve a one percent (1%) packet data error rate.
A signal to noise ratio (SNR) of eighteen and five tenths decibels (18.5 dB) is not achievable for IS-2000 based systems. Assuming that a 1xMC IS-2000 system could provide an 18.5 dB SNR, the 18.5 dB SNR would still not enable the system to achieve a one percent (1%) packet data error rate using 64-QAM modulation. This is because an ordinary Turbo encoding process can not achieve packet data error rates less than one percent (1%) when higher RF modulation is used (i.e., 64-QAM modulation or greater).
Therefore there is a need in the art for an improved channel encoder that is capable of providing a low packet data error rate when higher RF modulation is used. In particular, there is a need for an improved channel encoder that is capable of providing a packet data error rate less than one percent (1%) when a 64-QAM RF modulation is used.